In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly. Cleaning blades might also be used for the removal of toner from the surface of a detoning roll used to collect toner from the bristles of a brush cleaner, as shown for example in U.S. Pat. No. 4,819,026 to Longe et al, and assigned to the same assignee as the present application.
Although a preponderance of the toner forming the image is transferred to the paper during the transfer step, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom. Blade cleaning is a highly desirable method for removal of residual toner and debris (hereinafter, collectively referred to as "toner") from a charge retentive surface, because it provides a simple, inexpensive structure compared to the various fiber or magnetic brush cleaners that are well known in the dry electrophotography art. In a typical application, a relatively thin elastomeric blade member is provided and supported adjacent and transversely across the charge retentive surface with a blade edge chiseling or wiping toner from the surface. Subsequent to release of toner from the surface, the released toner accumulating adjacent the blade is transported away from the blade area by a toner transport arrangement or gravity. Unfortunately, blade cleaning suffers from certain deficiencies, primarily resulting from the frictional sealing contact which must be maintained between the blade and the charge retentive surface. Friction between the surfaces causes wearing away of the blade edge, and damaging wearing contact with the charge retentive surface. To reduce friction, various blade lubricating materials or toner lubricant additives have been proposed. However, lubricants tend to change the operational characteristics of the electrophotographic system undesirably.
In addition to the problem of wear, which is more or less predictable over time, blades are also subject to unpredictable failures. In normal operational configuration, with a coefficient of dynamic friction in the range of about 0.5 to 1.0, a blade cleaning edge or tip in sealing contact with the photoreceptor is tucked slightly as shown in FIG. 1. The blade is not in intimate contact with the photoreceptor, but slides on toner particles and lubricant, to maintain the sealing contact required for cleaning. In this configuration however, the blade may flatten toner that passes under the blade and cause impaction of toner on the surface. The impact from carrier beads remaining on the charge retentive surface subsequent to development may damage the blade, and sudden localized increases in friction between the blade and surface may cause the phenomenon of tucking, where the blade cleaning edge becomes tucked underneath the blade, losing the frictional sealing relationship required for blade cleaning. These problems require removal and replacement of the blade. Filming on the charge retentive surface may occur even though toner is cleaned from the surface. Filming, which can be a gradual buildup of material on the charge retentive surface can deteriorate image quality. Filming occurs either uniformly or streaking, due to deficiencies in blade cleaning, requiring the use of a lubricant and a balancing abrasion element to prevent filming.
U.S. Pat. No. 3,848,993 to Hasiotis and U.S. Pat. No. 4,426,151 to Aguro et al. describe cleaning blades with elastomer tips integrally mounted on flexible metal supports. JP-A 59-168483 teaches a chiseling metal blade with a knife edge and having a lubricant layer applied an upper surface so that the leading edge of the blade is provided with lubricant contacting the photoreceptor. The cleaning blade wears to provide lubricant at the contact between blade and photoreceptor. U.S. Pat. No. 4,264,191 to Gerbasi et al. suggests other combinations of laminated material, wherein a hard substrate material is laminated with a photoreceptor-contacting soft material having a relatively low coefficient of friction with respect to the photoreceptor material. Xerox Disclosure Journal, Vol. 1, No. 4, Apr. 1976, pg. 79, "Impregnated Poromeric Material Cleaning Blade", by P. Spencer and D. Fisher, suggests that a poromeric structure, such as a composite of polyester fibers bound together in polyurethane, may be impregnated with a lubricant. U.S. Pat. No. 2,404,689 to Carlsen et al. teaches a cleaning blade in a liquid ink device with a beveled blade having a chromium layer in contact with the surface. U.S. Pat. No. 2,361,554 to Lundbye shows another chromium plated blade for use in cleaning a liquid ink device.
While it might appear that a rigid metal blade might solve the problems of rigidity and wear in dry toner electrophotographic applications, in fact, the frictional contact required between the surface and blade quickly wears away the blade and any surface lubricants applied thereto. As the blade edge wears, it changes from a chiseling edge to a rounded or flattened surface which requires a high force to maintain the edge in sealing contact. While a beveled edge is useful in liquid toner applications, it is highly susceptible to damage and wear in dry toner applications. Accordingly it is desirable to maintain the square edge without wear. Additionally, wearing friction may generate toner fusing temperatures, causing toner to fuse to the blade, or the photoreceptor.
Xerox Disclosure Journal, Vol. 13, No. 2, Mar./Apr. 1988, pg. 101, "Low Friction Coating for Blade Cleaner Photoreceptor Supports", by Bruce Thayer, suggest that a support structure for the cleaning blade and in contact with the opposite side of a photoreceptor might be provided with an aluminum extrusion anodized and impregnated with a polytetrafluoroethylene, nickel-phosphorus impregnated with polymers, or porous bronze sintered onto the surface of the support with an overlayer of polytetrafluoroethylene lead.